Daring gap-year student Sam had been on a controlled tour there and was crossing into China when he noticed the disguised cargo arriving from the opposite direction.

Sam, who also filmed packages stacked behind the walls in an area patrolled by troops, said: “It looked like they were trying to hide whatever was on the train under straw.

“It was at a remote military compound and you can see guards around the train.”

Last year American student Otto Warmbier died after a spell in custody.

North Korea is being hit with crippling UN sanctions over Kim Jong-un's nuclear missile tests.

Among other restrictions, the sanctions limit imports of oil and petroleum products, but China has been accused of breaches.

Korea expert Catherine Jones, of the University of Warwick, said the straw “may be to conceal the contents from outside observers”.

She added: "It is not clear to me that these videos prove a violation of sanctions, as it is not clear what the contents of the train trucks is.

“The covering of trucks with straw may be to conceal the contents from outside observers.

“But it could be that these are not sanctioned goods, but are instead goods that the North Korean regime doesn’t want the population to see.

“There needs to be some further analysis of this footage before a conclusion can be drawn."

Catherine was keen to note that China has been accused of breaching sanctions against North Korea in the past.

Recent satellite images claimed to show a Chinese oil tanker illegally transferring oil to a North Korean ship in breach of the sanctions.

One picture, reportedly taken on October 19, shows a tanker called Ryesonggang connected to a Chinese vessel, The Chosun Ilbo reports.

China has denied any of its merchant ships were involved in sanction-breaking oil sales.

Last year, the hermit state carried out its sixth and biggest nuclear test and test-fired three intercontinental ballistic missiles and has shown no willingness to give up its ambitions.

In a sign of warming relations, North Korea agreed earlier this month to send a delegation to the Olympics, in the first formal talks between the rivals in about two years.

Its delegation at the February 9-25 games is to include officials, athletes, a cheering group, journalists, an art troupe and the taekwondo demonstration team.

SANCTIONS AGAINST NORTH KOREA

North Korea has been slapped with a number of sanctions over the years because its development of nuclear weapons and ballisitic missile technology have been sharply condemned.

The rogue state believes the US, South Korea and Japan pose direct threat to its existence.

In 1985, Kim Il-sung, leader at the time, signed the North up to the Nuclear Non-Proliferation Treaty, which aimed to achieve nuclear disarmamment, and prevent the spread of nuclear weapons technology.

But in 2003, the state wtihddrew claiming it was at risk of US aggression.

So what sanctions does North Korea face?

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